A 46-year old man was admitted complaining of dyspnea. Physical examination revealed superficial lymph nodes swelling, and coarse crackles over the lung. Chest X-ray film showed diffuse small granular shadows, suggesting diffuse panbronchiolitis (DPB). Peripheral blood smears showed cells with flower like nuclei. HTLV-I antibody was positive in the serum. He was diagnosed as having adult T-cell leukemia (ATL). Transbronchial lung biopsy showed diffuse infiltration of mononuclear cells around bronchioalveoli. The mononuclear cells stained positively for Pan T, CD2, CD3, CD4, CD5, CD25, and DNA from the cells showed HTLV-I provirus monoclonal integration. This is a rare case of ATL accompanied by DPB-like bronchioalveolar ATL cell infiltration.